Here's a place where I can post my thoughts on new papers, provide updates on my projects, and post info that will eventually be on my website The Theropod Database - http://theropoddatabase.com/ . It will center on theropods, but may delve into other topics as well such as phylogenetics.

Friday, November 19, 2010

Theropoda's new entry

To celebrate the new look of the Theropod Database Blog, here's the new entry for Theropoda for the upcoming update of the Database. It excludes the section discussing Gonipoda, Harpagosauria and Carnosauriformes, which was featured in a prior post. Unfortunately, my favored phylogenetic definition won't be the one set by the Phylocode, though theirs is better than the other three listed here at least.

Diagnosis- [upcoming]Other diagnoses- Marsh's (1881) original diagnosis consisted largely of plesiomorphies- carnivorous; limb bones hollow; digits with prehensile claws; digitigrade pes. The distal pubes are only fused in adult neotheropods. "Vertebrae more or less cavernous" refers to the extremely constricted dorsal centra of Allosaurus, which aren't present in most theropods. "Post-pubis present" probably refers to Allosaurus' elongate pubic boot, which is only present in some avetheropods.
Marsh (1884) added more plesiomorphies- premaxilla toothed; external nares placed anteriorly; large antorbital fossa; forelimbs short; propubic pelvis.
[more will be listed of course, though this will be a long process since so many authors have diagnosed Theropoda]

Comments- Marsh (1881) named Theropoda as a dinosaur suborder containing only the Allosauridae, in which he placed Allosaurus, Creosaurus and Labrosaurus (both of the latter now recognized as synonyms of Allosaurus). By 1884, Marsh had raised Theropoda to an order and expanded it to include all carnivorous dinosaurs, as well as what are today recognized as basal sauropodomorphs (often mixed with cranial elements of canivorous crurotarsans). This was the standard for many decades, as seen in Romer's (1956) classic work, in which theropods consist of coelurosaurs, carnosaurs and prosauropods. The monophyly of theropods was questioned by Huene (1914), who placed most of the larger taxa such as Allosaurus and Megalosaurus in Sauropodomorpha (his Pachypodosauria) while the smaller taxa (which he named Coelurosauria) had branched off earlier. In the 1960's, workers began to recognize the monophyly of coelurosaurs and carnosaurs to the exclusion of basal sauropodomorphs (e.g. Colbert, 1964). Paul (1984) was the first author to use a theropod phylogeny similar to todays, with deinonychosaurs (albeit paraphyletic), tyrannosaurids, allosaurids, Eustreptospondylus, Ceratosaurus and coelophysoids forming successively more distant sister taxa to birds. Gauthier's (1984) thesis also had a modern topology, with deinonychosaurs, ornithomimids, carnosaurs and ceratosaurs (the latter two improbably inclusive, containing tyrannosaurids and coelophysoids respectively) successively further from birds, and is the basis of our current nomenclature for major clades.

Theropoda defined- Gauthier (1986) was the first to phylogenetically define Theropoda, as "birds and all saurischians that are closer to birds than they are to sauropodomorphs." Variations on this definition have been most common, with Sereno (1998) using Neornithes and Saltasaurus, specified by Sereno (2004) as Passer domesticus and Saltasaurus loricatus. Holtz and Osmolska (2004) chose Cetiosaurus oxoniensis as the sauropodomorph specifier instead. However, this class of definition violates Phylocode Recommendation 11A- "Definitions of converted clade names should be stated in a way that attempts to capture the spirit of traditional use to the degree that it is consistent with the contemporary concept of monophyly." While birds are currently thought to be theropods, this was not the consensus until over a century after Theropoda was named. Similarly, Clarke et al.'s (2004) definition using Plateosaurus engelhardti as an external specifier is problematic since basal sauropodomorphs were often included in Theropoda until the 1960s. Kischlat (2000) suggested all taxa closer to Allosaurus than to Morosaurus, which is valid in using taxa Marsh (1881) and everyone since have recognized as being theropod and non-theropod. This definition is modified here by including the types species of each genus.

Ex-theropods- Numerous taxa (at least 130) have been incorrectly placed in Theropoda in the past, including ornithosuchids, poposaurids, most basal avemetatarsalians and basal sauropodomorphs, and many Triassic archosauriforms known only from teeth. This site will have an entire section devoted to ex-theropods, so they are not discussed further here.

References- Cope, 1866. [On the anomalous relations existing between the tibia and fibula in certain of the Dinosauria]. Proceedings of the Academy of Natural Sciences of Philadelphia. 18, 316-317.

Marsh, 1881. Principal characters of American Jurassic dinosaurs. Part V. American Journal of Science. 21, 417-423.

Marsh, 1884. Principal characters of American Jurassic dinosaurs. Part VIII. The order Theropoda. American Journal of Science. 27, 329-340.

Kischlat, 2000. Tecodoncios: A aurora dos Arcosaurios no Triassico. in Holz and De Rose (eds.). Paleontologia do Rio Grande do Sul. 273-316.

Clarke, Gauthier, de Queiroz, Joyce, Parham and Rowe, 2004. A phylogenetic nomenclature for the major clades of Amniota Haeckel 1866, with emphasis on Aves Linnaeus 1758. First International Phylogenetic Nomenclature Meeting, Abstracts. 30.

11 comments:

Oh, do you know what the Phylonyms definition of Theropoda is going to be? I headed the Saurpodomorpha definition, and made quite a few attempts to find out what the theropod people were doing so that we could make reflexive definitions of these sister groups, but never managed to get a definitive answer.

Yeah, but I don't know how much I can say since it's unpublished. I will say the definition isn't completely reflexive with your sauropodomorph one. If any of the Theropod Phylonyms authors want to comment, they're welcome to of course.

As for the Phylocode Sauropodomorpha definition, I dislike it because Saltasaurus loricatus was not even known when the clade was named, let alone included in it by Huene. It's so easy to choose taxa the original author included, I don't see why more definers don't do it. It's not like Saltasaurus is any less likely to be a sauropodomorph than Cetiosaurus, Camarasaurus, Diplodocus, Brachiosaurus or any of numerous other sauropods listed by Huene in 1932. My personal choice would be (Camarasaurus supremus <- Allosaurus fragilis).

Note that Tyrannosaurus was sometimes placed in Coelurosauria sensu Huene, which would leave carnosaurs sensu Huene as sauropodomorphs given your definition (due to Huene's Pachypodosauria). Not likely to be true, I agree, but it's so easy to make definitions that agree with all prior hypotheses, why not do it now that we have the chance?

Mickey, I won't go into all the reasons here why we chose the definition we did. But I will say that there are a LOT of desiderata in choosing anchor taxa, and it's generally impossible to satisfy then all; and that where we ended up is not just my choice, it's the result of extended discussion between a whole bunch of authors who know their stuff.

"[...] it's so easy to make definitions that agree with all prior hypotheses, why not do it now that we have the chance?"

Mickey's words should be underlined, italicized, bolded and coloured. And then sent to all authors of phylogenetic definitions (then again and... then again). I'd like to know how many people were involved in creating phylogenetic definitions for the Companion Volume and how many of them considered more hypotheses than their own (or the newest one).

(Just to make it clear, that's not meant to be a reaction to Mike et al.'s definition of Sauropodomorpha. While I would use something else [D. longus <- A. fragilis, probably], it's still far better than many other definitions.)

Andrea, would it be possible to tell me (by mail, if you don't want to write about it publicly: daniel.madzia[at]gmail.com) how did you define Allosauroidea? I would appreciate it a lot.

Daniel, I did not define Allosauroidea. I was invloved in the Theropoda paper of the Phylonyms, where we defined only that name.

Regarding Allosauroidea, I would follow the "Allosaurus fragilis + Sinraptor dongi" definition by Padian and Hutchinson, 1997.In my opinion, the other definition of the name Allosauroidea: "all theropods closer to Allosaurus fragilis than Passer domesticus", used by Sereno (1998) and others, refers to a different clade: Carnosauria. If you don't like the use of birds in non-avian theropod clade name definitions, Coelurus fragilis may be a good alternative for the definition of Carnosauria (and its sister-taxon Coelurosauria, defined as "Coelurus > Allosaurus").

Thanks for the information, Andrea. I would follow Padian & Hutchinson's definition too (http://phylonom.wildprehistory.org/viewtopic.php?f=18&t=2) so I find it pity that you (and your co-authors) didn't define it:o) Do you know if Allosauroidea is defined in the Companion Volume (and if yes, do you know who was working on it)?

Just to clarify Andrea's comment, only major clades like Theropoda and Sauropodomorpha are being defined in Phylonyms. For the others we'll have to depend on subsequent workers. Maybe I should write a post of recommended definitions...